Is it ok to share your Trello developer API key that is generated at https://trello.com/1/appKey/generate? See the documentation for more details. I assume this key would be visible in any application you publish but I'd rather ask a stupid question than make stupid mistake.
Consensus is you should not share your key. Here are a few examples of using the Trello API:
https://github.com/GraemeF/trello
https://gist.github.com/1893771
You'll need to have them provide their API key and a token.